I could...but i couldn't

I could,
Compete with the other boys,
To win your heart,
To be your hero,

I could,
Not to listen to anyone,
Pass any obstacle,
Break any rules,

I could,
Walk for God knows how long,
to walk in winter,
even without a coat,

I could do anything,
Just to be by your side,
To hold you in my arms,
To never leave your side,

Ask me to jump i jump,
Ask me to wait i wait,
Ask me to come i will be there,
Ask me anythin but...

There is one thing i could not do,
When you ask me to leave...